/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.messaging.simp.annotation.support;

import java.lang.annotation.Annotation;
import java.security.Principal;
import java.util.Map;

import org.springframework.core.MethodParameter;
import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.lang.Nullable;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.MessageHeaders;
import org.springframework.messaging.handler.DestinationPatternsMessageCondition;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.messaging.handler.annotation.support.DestinationVariableMethodArgumentResolver;
import org.springframework.messaging.handler.invocation.HandlerMethodReturnValueHandler;
import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
import org.springframework.messaging.simp.SimpMessageSendingOperations;
import org.springframework.messaging.simp.SimpMessageType;
import org.springframework.messaging.simp.SimpMessagingTemplate;
import org.springframework.messaging.simp.annotation.SendToUser;
import org.springframework.messaging.simp.user.DestinationUserNameProvider;
import org.springframework.messaging.support.MessageHeaderInitializer;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;
import org.springframework.util.PropertyPlaceholderHelper;
import org.springframework.util.PropertyPlaceholderHelper.PlaceholderResolver;
import org.springframework.util.StringUtils;

/**
 * A {@link HandlerMethodReturnValueHandler} for sending to destinations specified in a
 * {@link SendTo} or {@link SendToUser} method-level annotations.
 *
 * <p>The value returned from the method is converted, and turned to a {@link Message} and
 * sent through the provided {@link MessageChannel}. The message is then enriched with the
 * session id of the input message as well as the destination from the annotation(s).
 * If multiple destinations are specified, a copy of the message is sent to each destination.
 *
 * @author Rossen Stoyanchev
 * @author Sebastien Deleuze
 * @since 4.0
 */
public class SendToMethodReturnValueHandler implements HandlerMethodReturnValueHandler {

    private final SimpMessageSendingOperations messagingTemplate;

    private final boolean annotationRequired;

    private String defaultDestinationPrefix = "/topic";

    private String defaultUserDestinationPrefix = "/queue";

    private PropertyPlaceholderHelper placeholderHelper = new PropertyPlaceholderHelper("{", "}", null, false);

    @Nullable
    private MessageHeaderInitializer headerInitializer;


    public SendToMethodReturnValueHandler(SimpMessageSendingOperations messagingTemplate, boolean annotationRequired) {
        Assert.notNull(messagingTemplate, "'messagingTemplate' must not be null");
        this.messagingTemplate = messagingTemplate;
        this.annotationRequired = annotationRequired;
    }


    /**
     * Configure a default prefix to add to message destinations in cases where a method
     * is not annotated with {@link SendTo @SendTo} or does not specify any destinations
     * through the annotation's value attribute.
     * <p>By default, the prefix is set to "/topic".
     */
    public void setDefaultDestinationPrefix(String defaultDestinationPrefix) {
        this.defaultDestinationPrefix = defaultDestinationPrefix;
    }

    /**
     * Return the configured default destination prefix.
     *
     * @see #setDefaultDestinationPrefix(String)
     */
    public String getDefaultDestinationPrefix() {
        return this.defaultDestinationPrefix;
    }

    /**
     * Configure a default prefix to add to message destinations in cases where a
     * method is annotated with {@link SendToUser @SendToUser} but does not specify
     * any destinations through the annotation's value attribute.
     * <p>By default, the prefix is set to "/queue".
     */
    public void setDefaultUserDestinationPrefix(String prefix) {
        this.defaultUserDestinationPrefix = prefix;
    }

    /**
     * Return the configured default user destination prefix.
     *
     * @see #setDefaultUserDestinationPrefix(String)
     */
    public String getDefaultUserDestinationPrefix() {
        return this.defaultUserDestinationPrefix;
    }

    /**
     * Configure a {@link MessageHeaderInitializer} to apply to the headers of all
     * messages sent to the client outbound channel.
     * <p>By default this property is not set.
     */
    public void setHeaderInitializer(@Nullable MessageHeaderInitializer headerInitializer) {
        this.headerInitializer = headerInitializer;
    }

    /**
     * Return the configured header initializer.
     */
    @Nullable
    public MessageHeaderInitializer getHeaderInitializer() {
        return this.headerInitializer;
    }


    @Override
    public boolean supportsReturnType(MethodParameter returnType) {
        return (returnType.hasMethodAnnotation(SendTo.class) ||
                AnnotatedElementUtils.hasAnnotation(returnType.getDeclaringClass(), SendTo.class) ||
                returnType.hasMethodAnnotation(SendToUser.class) ||
                AnnotatedElementUtils.hasAnnotation(returnType.getDeclaringClass(), SendToUser.class) ||
                !this.annotationRequired);
    }

    @Override
    public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType, Message<?> message)
            throws Exception {

        if (returnValue == null) {
            return;
        }

        MessageHeaders headers = message.getHeaders();
        String sessionId = SimpMessageHeaderAccessor.getSessionId(headers);
        PlaceholderResolver varResolver = initVarResolver(headers);
        Object annotation = findAnnotation(returnType);

        if (annotation instanceof SendToUser) {
            SendToUser sendToUser = (SendToUser) annotation;
            boolean broadcast = sendToUser.broadcast();
            String user = getUserName(message, headers);
            if (user == null) {
                if (sessionId == null) {
                    throw new MissingSessionUserException(message);
                }
                user = sessionId;
                broadcast = false;
            }
            String[] destinations = getTargetDestinations(sendToUser, message, this.defaultUserDestinationPrefix);
            for (String destination : destinations) {
                destination = this.placeholderHelper.replacePlaceholders(destination, varResolver);
                if (broadcast) {
                    this.messagingTemplate.convertAndSendToUser(
                            user, destination, returnValue, createHeaders(null, returnType));
                } else {
                    this.messagingTemplate.convertAndSendToUser(
                            user, destination, returnValue, createHeaders(sessionId, returnType));
                }
            }
        } else {
            SendTo sendTo = (SendTo) annotation;  // possibly null
            String[] destinations = getTargetDestinations(sendTo, message, this.defaultDestinationPrefix);
            for (String destination : destinations) {
                destination = this.placeholderHelper.replacePlaceholders(destination, varResolver);
                this.messagingTemplate.convertAndSend(destination, returnValue, createHeaders(sessionId, returnType));
            }
        }
    }

    @Nullable
    private Object findAnnotation(MethodParameter returnType) {
        Annotation[] anns = new Annotation[4];
        anns[0] = AnnotatedElementUtils.findMergedAnnotation(returnType.getExecutable(), SendToUser.class);
        anns[1] = AnnotatedElementUtils.findMergedAnnotation(returnType.getExecutable(), SendTo.class);
        anns[2] = AnnotatedElementUtils.findMergedAnnotation(returnType.getDeclaringClass(), SendToUser.class);
        anns[3] = AnnotatedElementUtils.findMergedAnnotation(returnType.getDeclaringClass(), SendTo.class);

        if (anns[0] != null && !ObjectUtils.isEmpty(((SendToUser) anns[0]).value())) {
            return anns[0];
        }
        if (anns[1] != null && !ObjectUtils.isEmpty(((SendTo) anns[1]).value())) {
            return anns[1];
        }
        if (anns[2] != null && !ObjectUtils.isEmpty(((SendToUser) anns[2]).value())) {
            return anns[2];
        }
        if (anns[3] != null && !ObjectUtils.isEmpty(((SendTo) anns[3]).value())) {
            return anns[3];
        }

        for (int i = 0; i < 4; i++) {
            if (anns[i] != null) {
                return anns[i];
            }
        }

        return null;
    }

    @SuppressWarnings("unchecked")
    private PlaceholderResolver initVarResolver(MessageHeaders headers) {
        String name = DestinationVariableMethodArgumentResolver.DESTINATION_TEMPLATE_VARIABLES_HEADER;
        Map<String, String> vars = (Map<String, String>) headers.get(name);
        return new DestinationVariablePlaceholderResolver(vars);
    }

    @Nullable
    protected String getUserName(Message<?> message, MessageHeaders headers) {
        Principal principal = SimpMessageHeaderAccessor.getUser(headers);
        if (principal != null) {
            return (principal instanceof DestinationUserNameProvider ?
                    ((DestinationUserNameProvider) principal).getDestinationUserName() : principal.getName());
        }
        return null;
    }

    protected String[] getTargetDestinations(@Nullable Annotation annotation, Message<?> message, String defaultPrefix) {
        if (annotation != null) {
            String[] value = (String[]) AnnotationUtils.getValue(annotation);
            if (!ObjectUtils.isEmpty(value)) {
                return value;
            }
        }

        String name = DestinationPatternsMessageCondition.LOOKUP_DESTINATION_HEADER;
        String destination = (String) message.getHeaders().get(name);
        if (!StringUtils.hasText(destination)) {
            throw new IllegalStateException("No lookup destination header in " + message);
        }

        return (destination.startsWith("/") ?
                new String[]{defaultPrefix + destination} : new String[]{defaultPrefix + '/' + destination});
    }

    private MessageHeaders createHeaders(@Nullable String sessionId, MethodParameter returnType) {
        SimpMessageHeaderAccessor headerAccessor = SimpMessageHeaderAccessor.create(SimpMessageType.MESSAGE);
        if (getHeaderInitializer() != null) {
            getHeaderInitializer().initHeaders(headerAccessor);
        }
        if (sessionId != null) {
            headerAccessor.setSessionId(sessionId);
        }
        headerAccessor.setHeader(SimpMessagingTemplate.CONVERSION_HINT_HEADER, returnType);
        headerAccessor.setLeaveMutable(true);
        return headerAccessor.getMessageHeaders();
    }


    @Override
    public String toString() {
        return "SendToMethodReturnValueHandler [annotationRequired=" + annotationRequired + "]";
    }


    private static class DestinationVariablePlaceholderResolver implements PlaceholderResolver {

        @Nullable
        private final Map<String, String> vars;

        public DestinationVariablePlaceholderResolver(@Nullable Map<String, String> vars) {
            this.vars = vars;
        }

        @Override
        @Nullable
        public String resolvePlaceholder(String placeholderName) {
            return (this.vars != null ? this.vars.get(placeholderName) : null);
        }
    }

}
